Currently, a liquid crystal display device is one of widely used display devices. FIG. 1 schematically shows a cross-sectional view of a conventional liquid crystal display device. As shown in FIG. 1, the basic structure of a liquid crystal display device is such that a liquid crystal cell 13 is placed between two parallel glass substrates (11, 12), a thin film transistor (TFT) 121 is positioned on the lower glass substrate 12 (also referred to as an array substrate), color blocks (including red (R), green (G) and blue (B)) are positioned on the upper glass substrate 11 (also referred to as a color film substrate), and a backlight unit 14 is positioned under the lower glass substrate 12. White light 141 emitted by the backlight unit sequentially passes through the lower glass substrate 12, the liquid crystal layer 13 and the upper glass substrate 11, thereby presenting a full color display and a grayscale luminance.